JP2013156501A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device capable of reducing that a recording sheet is wrinkled while maintaining a cylindrical member at a straight state in fixation.SOLUTION: A fixing device is the one for performing thermal fixation of a developer image transferred on a recording sheet, and includes: a flexible cylindrical member; a heater disposed inside the cylindrical member; a nip plate 130 which is in slide contact with the inner peripheral surface of the cylindrical member, and is heated by the heater; and a pressure roller 150 (backup roller) which sandwiches the cylindrical member between the pressure roller 150 and the nip plate 130. The nip plate 130 curves so that the center part in the axis direction of the cylindrical member is separated from the pressure roller 150 farther than at both ends at least in fixation. The pressure roller 150 is a concave roller in which a diameter of the center part in the axis direction is smaller than diameters of both the ends.

Description

  The present invention relates to a fixing device for thermally fixing a developer image transferred to a recording sheet.

  2. Description of the Related Art Conventionally, as a fixing device used in an electrophotographic image forming apparatus, a fixing device including a cylindrical member, a ceramic heater, a heater frame, and a backup roller is known (for example, see Patent Document 1). The ceramic heater is disposed so as to be in sliding contact with the inner peripheral surface of the cylindrical member, and heats the cylindrical member. The backup roller has a straight shape and sandwiches the cylindrical member with the ceramic heater. The heater frame is disposed on the side opposite to the backup roller of the ceramic heater and supports the heater frame.

  In this fixing device, the portion of the heater frame that faces the backup roller has a concave shape that is curved so that the central portion in the axial direction of the cylindrical member is farther from the backup roller than both ends. Thereby, at the time of fixing, when both end portions in the axial direction of the heater frame are pressed toward the backup roller, the pressure applied between the ceramic heater and the backup roller is larger at the both end portions in the axial direction than at the central portion. Become. Therefore, the conveyance speed of both ends of the recording sheet conveyed between the cylindrical member and the backup roller is increased, and the central portion of the recording sheet is pulled toward both ends. As a result, wrinkles on the recording sheet can be reduced.

US Pat. No. 6,266,510

  By the way, in the above-described fixing device, the backup roller has a straight shape and only the heater frame has a concave shape. Therefore, in order to properly adjust the pressure difference between the ceramic heater and the backup roller as described above, the heater The amount of dents in the frame must be increased. However, if the dent amount of the heater frame is large, it becomes difficult to keep the cylindrical member in a straight state during operation.

  Therefore, an object of the present invention is to provide a fixing device that can reduce wrinkles on a recording sheet while keeping a cylindrical member straight during fixing.

In order to achieve the above object, a fixing device of the present invention is a fixing device for thermally fixing a developer image transferred to a recording sheet, and includes a flexible cylindrical member and an inner portion of the cylindrical member. And a nip plate that is in sliding contact with the inner peripheral surface of the cylindrical member and is heated by the heater, and a backup roller that sandwiches the cylindrical member between the nip plate.
The nip plate is curved so that the central portion in the axial direction of the cylindrical member is farther from the backup roller than both ends at least during fixing.
The backup roller is a concave roller in which the diameter of the central portion in the axial direction is smaller than the diameter of both end portions.

  According to the fixing device configured as described above, it is possible to reduce the dent amount of the nip plate as compared with the case where only the nip plate is in a concave shape and the backup roller is in a straight shape. Thereby, it is easy to keep the cylindrical member sandwiched between the nip plate and the backup roller in a straight state. Further, at the time of fixing, the pressure applied between the nip plate and the backup roller is larger at both ends in the axial direction than at the center, so that the recording sheet is pulled toward both ends in the axial direction, and the recording sheet It is difficult for the wrinkles to move toward the center in the axial direction.

The fixing device described above may further include a stay that is disposed on the side opposite to the backup roller side of the nip plate and has a support surface that supports the nip plate.
In this case, the support surface may be curved such that the central portion in the axial direction is farther from the backup roller than both ends.

  In the fixing device including the stay described above, it is desirable that the nip plate bends by being deformed following the shape of the support surface.

  According to the fixing device configured in this way, the molding is easier than in the case where the nip plate itself has a previously curved shape.

  The stay described above may be formed in a substantially U-shape that is asymmetrical when viewed from the axial direction.

In the fixing device having the stay described above, the heater is a heating element that emits radiant heat, and a reflector that reflects the radiant heat from the heater toward the nip plate is provided between the heater and the stay. The reflecting plate may have a supported portion that is sandwiched between the nip plate and the stay.
In this case, the supported portion is curved so that the central portion in the axial direction is farther from the backup roller than both ends at least during fixing.

  In the fixing device described above, the cylindrical member may be made of metal.

  In the fixing device described above, the backup roller may include a metal shaft and a rubber layer that covers the outer periphery of the shaft, and the shaft may have a straight shape.

  According to the present invention, the amount of dent in the nip plate can be reduced as compared with the case where only the nip plate is in a concave shape and the backup roller is in a straight shape. Thereby, it is easy to keep the cylindrical member sandwiched between the nip plate and the backup roller in a straight state. Further, at the time of fixing, the pressure applied between the nip plate and the backup roller is larger at both ends in the axial direction of the cylindrical member than at the center, so that the recording sheet is pulled toward both ends in the axial direction. It is hard to get wrinkles on the recording sheet.

1 is a diagram illustrating a schematic configuration of a laser printer including a fixing device according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a fixing device. It is a perspective view which shows a halogen lamp, a nip plate, a reflecting plate, a pressure roller, and a stay. It is a figure which shows the reflecting plate and nip plate, pressure roller, and urging member which were assembled | attached to the stay. FIG. 10 is an explanatory diagram illustrating a sheet conveyed through the fixing device. FIG. 9 is a cross-sectional view illustrating a fixing device according to a modification.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, a schematic configuration of the laser printer 1 (image forming apparatus) including the fixing device 100 according to an embodiment of the present invention will be described, and then a detailed configuration of the fixing device 100 will be described.

<Schematic configuration of laser printer>
As shown in FIG. 1, the laser printer 1 includes a main body housing 2 in which a paper sheet 3 as an example of a recording sheet is fed, an exposure device 4, and a toner image (developer) on the paper P. And the fixing device 100 for thermally fixing the toner image on the paper P.

  In the following description, the direction will be described with reference to the user who uses the laser printer 1. That is, the right side in FIG. 1 is “front”, the left side is “rear”, the front side is “left”, and the back side is “right”. Also, the vertical direction in FIG.

  The paper feed unit 3 is provided in the lower part of the main body housing 2, and includes a paper feed tray 31 that accommodates the paper P, a paper pressing plate 32 that lifts the front side of the paper P, a paper feed roller 33, and a paper feed pad 34. And paper dust removing rollers 35 and 36 and a registration roller 37 are mainly provided. The paper P in the paper feed tray 31 is brought close to the paper feed roller 33 by the paper pressing plate 32 and separated one by one by the paper feed roller 33 and the paper feed pad 34, and the paper dust removing rollers 35, 36 and the registration roller 37. Then, it is conveyed toward the process cartridge 5.

  The exposure apparatus 4 is arranged at the upper part in the main body housing 2 and mainly includes a laser light emitting unit (not shown), a polygon mirror 41 that is rotationally driven, lenses 42 and 43, and reflecting mirrors 44, 45, and 46. In preparation. In the exposure apparatus 4, the laser light (see the chain line) based on the image data emitted from the laser light emitting part is reflected or passed through the polygon mirror 41, the lens 42, the reflecting mirrors 44 and 45, the lens 43 and the reflecting mirror 46 in this order. The surface of the photosensitive drum 61 is scanned at high speed.

  The process cartridge 5 is disposed below the exposure apparatus 4 and is detachably mounted on the main body housing 2 through an opening formed when the front cover 21 provided on the main body housing 2 is opened. Yes. The process cartridge 5 includes a drum unit 6 and a developing unit 7.

  The drum unit 6 mainly includes a photosensitive drum 61, a charger 62, and a transfer roller 63. The developing unit 7 is configured to be detachably attached to the drum unit 6, and includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a toner that contains toner (developer). The housing part 74 is mainly provided.

  In the process cartridge 5, the surface of the photosensitive drum 61 is uniformly charged by the charger 62 and then exposed by high-speed scanning of the laser light from the exposure device 4, whereby image data is transferred onto the photosensitive drum 61. An electrostatic latent image based on is formed. Further, the toner in the toner container 74 is supplied to the developing roller 71 via the supply roller 72 and enters between the developing roller 71 and the layer thickness regulating blade 73 to form a thin layer of a certain thickness on the developing roller 71. It is carried on.

  The toner carried on the developing roller 71 is supplied from the developing roller 71 to the electrostatic latent image formed on the photosensitive drum 61. As a result, the electrostatic latent image is visualized and a toner image is formed on the photosensitive drum 61. Thereafter, the paper P is conveyed between the photosensitive drum 61 and the transfer roller 63, whereby the toner image on the photosensitive drum 61 is transferred onto the paper P.

  The fixing device 100 is provided behind the process cartridge 5. The toner image (toner) transferred onto the paper P is thermally fixed onto the paper P by passing through the fixing device 100. The paper P on which the toner image is thermally fixed is discharged onto the paper discharge tray 22 by the transport rollers 23 and 24.

<Detailed configuration of fixing device>
2 and 3, the fixing device 100 includes a fixing belt 110 as an example of a cylindrical member, a halogen lamp 120 as an example of a heater, a nip plate 130, a reflection plate 140, and a backup roller. As an example, a pressure roller 150 and a stay 160 are provided.

  The fixing belt 110 is an endless (cylindrical) stainless steel belt having heat resistance and flexibility, and both ends thereof are guided to rotate by guide members (not shown). The fixing belt 110 has a straight shape whose outer diameter is substantially constant in the axial direction of the fixing belt 110, that is, in the left-right direction.

  The halogen lamp 120 is a heating element that generates a known radiant heat that heats the toner on the paper P by heating the nip plate 130 and the fixing belt 110, and the fixing belt 110 and the nip plate 130 are disposed inside the fixing belt 110. They are arranged at a predetermined interval from the inside.

  The nip plate 130 is a plate-like member that receives radiant heat from the halogen lamp 120, and is disposed so as to be in sliding contact with the inner surface of the cylindrical fixing belt 110. The nip plate 130 transmits the radiant heat received from the halogen lamp 120 to the toner on the paper P via the fixing belt 110.

  The nip plate 130 has a thermal conductivity higher than that of a steel stay 160 described later, and is configured to be planar, for example, an aluminum plate. The nip plate 130 is formed with a thickness that allows bending deformation.

  The reflection plate 140 is a member that reflects radiant heat from the halogen lamp 120 (mainly radiant heat radiated in the front-rear direction or the upward direction) toward the nip plate 130 (the upper surface of the nip plate 130). The reflection plate 140 is disposed at a predetermined interval from the halogen lamp 120 so as to surround the halogen lamp 120 inside the fixing belt 110, more specifically, between the halogen lamp 120 and a stay 160 described later. .

  By collecting the radiant heat from the halogen lamp 120 to the nip plate 130 with such a reflector 140, the radiant heat from the halogen lamp 120 can be used efficiently, and the nip plate 130 and the fixing belt 110 can be heated quickly. Can do.

  The reflection plate 140 is formed by curving an aluminum plate or the like in a substantially U shape in cross section, for example, having a high infrared and far infrared reflectance. More specifically, the reflecting plate 140 includes a reflecting portion 141 having a curved shape (substantially U shape in cross section), and a flange portion 142 as an example of a supported portion that extends from both ends of the reflecting portion 141 along the outer side in the front-rear direction. It has mainly. In order to increase the thermal reflectance, the reflection plate 140 may be formed using a mirror-finished aluminum plate or the like. Moreover, although the flange part 142 is formed in planar shape, it can be deform | transformed so that the reflection plate 140 whole may be bent by deforming.

  The pressure roller 150 is an elastically deformable member and is disposed below the nip plate 130. The pressure roller 150 sandwiches the fixing belt 110 with the nip plate 130 in an elastically deformed state.

  The pressure roller 150 is a concave roller in which the diameter at the center in the left-right direction is smaller than the diameter at both ends. Specifically, as illustrated in FIG. 4, the pressure roller 150 includes a metal shaft 151 and a rubber layer 152 that covers the outer periphery of the shaft 151. The shaft 151 is formed in a straight shape having a substantially constant diameter across the left-right direction. The rubber layer 152 is thicker at both ends in the left-right direction than at the center so that the outer diameter at both ends in the left-right direction is larger than the outer diameter at the center. .

  The rubber layer 152 is manufactured by using a mold having a hollow cylindrical cavity as an example. Since the rubber layer 152 is elastically deformable, even if it has a concave shape, it can be extracted from the mold.

  The pressure roller 150 is configured to be driven to rotate by a driving force transmitted from a motor (not shown) provided in the main body housing 2, and to rotate with the fixing belt 110 (or paper P). The fixing belt 110 is driven to rotate by the frictional force. As a result, the sheet P on which the toner image is transferred is conveyed between the pressure roller 150 and the heated fixing belt 110 so that the toner image (toner) is thermally fixed.

  2 and 3, the stay 160 is a member that ensures the rigidity of the nip plate 130 by supporting both end portions of the nip plate 130 in the front-rear direction via the flange portion 142 of the reflection plate 140. The stay 160 has a shape (substantially U shape in cross section) along the outer surface shape of the reflecting plate 140 (reflecting portion 141) and is disposed so as to cover the reflecting plate 140. Such a stay 160 has relatively high rigidity, for example, is formed by bending a steel plate or the like into a substantially U-shaped cross-sectional view that is symmetric.

  The stay 160 is disposed above the reflecting plate 140 and has a planar upper wall 161, a front wall 162 that extends downward from the front end of the upper wall 161, and a downward direction from the rear end of the upper wall 161. And a rear wall 163 extending in the direction. The lower end surfaces of the front wall 162 and the rear wall 163 form a support surface 164 that supports the flange portion 142 of the nip plate 130 and the reflection plate 140.

  As shown in FIG. 3, the front wall 162 and the rear wall 163 of the stay 160 are such that the distance from the upper wall 161 to the support surface 164 at the center in the left-right direction is the distance from the upper wall 161 to the support surface 164 at both ends. It is smaller than before. That is, the support surface 164 has a concave shape that is curved so that the central portion in the left-right direction is farther from the pressure roller 150 than both ends.

  When the stay 160 is manufactured, for example, a blank material obtained by punching out a portion corresponding to the support surface 164 at the lower end of the front wall 162 and the rear wall 163 of the stay 160 to have a desired concave curved surface by a trim mold. Can be manufactured in a U shape.

Here, the concave shape in the present embodiment will be described.
As shown in FIG. 4, the concave amount X in the concave shape of the pressure roller 150 is obtained when the outer diameters at the left and right ends of the pressure roller 150 are φA and φB, respectively, and the outer diameter at the center is φC. = (ΦA + φB) / 2−φC. In addition, the concave amount Y in the concave shape of the stay 160 is the left and right center portions of the front wall 162 and the rear wall 163 when the left and right ends of the front wall 162 and the rear wall 163 of the stay 160 are placed on a plane. And distance D.

For example, in a state where the pressure roller 150 and the nip plate 130 are separated, the dent amount X of the pressure roller 150 is 0.1 to 0.2 mm, and the dent amount Y of the stay 160 is 0 to 0.00. 1 mm. That is, the dent amount X of the pressure roller 150 is larger than the dent amount Y of the stay 160.
Regarding the pressure roller 150, the straight shape in the present embodiment is a dent amount X of less than 0.050 mm, and the concave shape is a dent amount X having a dent amount X of 0.051 mm or more. Further, regarding the stay 160, the straight shape in the present embodiment has a dent amount Y of less than 0.001 mm, and the concave shape has a dent amount Y of 0.001 mm or more. 0.01 mm or more, more preferably 0.05 mm or more.

According to the above, the following operations and effects can be obtained in the present embodiment.
As shown in FIG. 2, the nip plate 130 and the reflection plate 140 are assembled to the stay 160 so that the flange portion 142 of the reflection plate 140 is sandwiched between the support surface 164 of the stay 160 and the nip plate 130. The stay 160 is urged toward the pressure roller 150 by the urging members 200 provided at both ends in the left-right direction as shown in FIG. 4 at the time of fixing.

  In this state, when the halogen lamp 120 is turned on at the time of fixing, the flange portion 142 of the nip plate 130 and the reflection plate 140 is deformed following the support surface 164 of the stay 160, and the central portion in the left-right direction is added more than both ends. Curved away from the pressure roller 150.

  As a result, the pressure applied between the nip plate 130 and the pressure roller 150 is greater at both ends than at the center in the left-right direction. When the paper P is conveyed in this state, as shown in FIG. 5, the nip region NP sandwiched between the fixing belt 110 and the pressure roller 150 of the paper P has both ends of the paper P in the width direction (left-right direction) rather than the central portion. The part is wider in the transport direction (front-rear direction). Thereby, the conveyance speed of the both ends in the left-right direction of the paper P becomes faster than the central part. Accordingly, the portion of the paper P that enters the nip region NP (between the fixing belt 110 and the pressure roller 150) (the upstream portion with respect to the nip region NP) is at both ends in the left-right direction of the nip region NP. It is pulled to the part and the center part is in a stretched state.

  In this way, the sheet P enters the nip region NP (between the fixing belt 110 and the pressure roller 150) with the central portion in the width direction stretched, so that wrinkles on the sheet P are reduced. be able to.

  Further, by curving the nip plate 130 and further forming the pressure roller 150 in a concave shape, the dent amount of the nip plate 130 and the pressure roller 150 can be made smaller than when only the nip plate 130 is curved. Can do. As a result, the fixing belt 110 sandwiched between the nip plate 130 and the pressure roller 150 is not greatly deformed, and can be rotated while maintaining a straight state.

  Further, when the pressure roller 150 is heated, the central portion in the left-right direction expands and approaches a straight shape. Therefore, by setting the dent amount X of the pressure roller 150 to be larger than the dent amount Y of the stay 160, the dent amount Y of the stay 160 is set to be larger than the dent amount X of the pressure roller 150. The fixing belt 110 sandwiched between the pressure roller 150 and the nip plate 130 is not greatly deformed, and can be rotated while maintaining a straight state.

  Since the nip plate 130 is curved by deforming in accordance with the shape of the support surface 164 of the stay 160, the nip plate 130 can be manufactured compared to the case where the nip plate 130 itself is curved in advance. Easy.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention.

  In the embodiment, the stay 160 is formed in a substantially U-shape that is symmetrical to the left and right, but the present invention is not limited to this. For example, as shown in FIG. 6, the stay 160 may be formed in a substantially U shape that is asymmetrical to the left and right.

  Specifically, in the stay 160, the vertical length of the front wall 262 extending downward from the front end of the upper wall 161 is larger than the vertical length of the rear wall 263 extending downward from the rear end of the upper wall 161. It is getting smaller. A flange 264 that extends to the front side is formed at the lower end of the front wall 262.

  In the stay 160, for example, a support surface 265 curved so that the central portion in the left-right direction is closer to the upper wall than both ends is formed by bending the flange 264, and the lower end surface of the rear wall 263 is pressed. Thus, the support surface 266 that is curved so that the central portion in the left-right direction is closer to the upper wall than both ends is formed.

  In this way, by forming the stay 160 in a substantially U-shape that is asymmetrical to the left and right, the front end portion of the nip plate 230 can be bent upward. Specifically, the nip plate 230 includes a base portion 231 formed in a planar shape and a bent portion 232 bent upward from the front end of the base portion 231.

  In the nip plate 230, the rear end portion 231 </ b> A of the base portion 231 is supported by the support surface 266 of the stay 260 via the flange portion 142 of the reflecting plate 140, and the end surface 232 </ b> A of the bent portion 232 is supported by the flange of the reflecting plate 140. It is supported by the support surface 265 of the stay 260 via the portion 142.

  In this way, the front end portion of the nip plate 230 is bent, so that the stay 160 is asymmetrically substantially U-shaped and the nip plate 230 is not provided with the bent portion 232 (see the two-dot chain line). Since the distance between the fixing belt 110 and the pressure roller 150 is larger in front of the pressure contact portion between the belt 110 and the pressure roller 150, that is, upstream in the conveyance direction of the paper P, the paper P is conveyed at any angle. Even if it comes, it is easy to guide between the fixing belt 110 and the pressure roller 150.

  In the above-described embodiment, the flange portion 142 of the nip plate 130 and the reflecting plate 140 is configured to deform following the shape of the support surface 164 of the stay 160 and is curved at least during fixing. The invention is not limited to this, and the flange portion and the nip plate of the reflecting plate may be formed in advance in a curved shape so that the central portion in the left-right direction is farther from the pressure roller 150 than both ends.

  Moreover, in the said embodiment, although the cylindrical member was a product made from stainless steel, ie, metal, this invention is not limited to this, The cylindrical member may be formed from resin.

  In the embodiment, the halogen lamp 120 is exemplified as the heater. However, the present invention is not limited to this, and may be, for example, a carbon heater or an IH heater.

  In the embodiment, the paper P such as plain paper or postcard is exemplified as the recording sheet, but the present invention is not limited to this, and may be, for example, an OHP sheet.

DESCRIPTION OF SYMBOLS 1 Laser printer 100 Fixing apparatus 110 Fixing belt 120 Halogen lamp 130 Nip plate 140 Reflecting plate 142 Flange part 150 Pressure roller 151 Shaft 152 Rubber layer 160 Stay 164 Support surface P Paper

Claims (7)

A fixing device for thermally fixing a developer image transferred to a recording sheet,
A flexible tubular member;
A heater disposed inside the tubular member;
A nip plate that is in sliding contact with the inner peripheral surface of the cylindrical member and is heated by the heater;
A backup roller that sandwiches the cylindrical member with the nip plate, and
The nip plate is curved so that at least at the time of fixing, the central portion in the axial direction of the cylindrical member is farther from the backup roller than both ends,
The fixing device according to claim 1, wherein the backup roller is a concave roller having a diameter at a central portion in the axial direction smaller than a diameter at both ends. A stay that is disposed on the opposite side of the nip plate from the backup roller side and has a support surface that supports the nip plate;
The fixing device according to claim 1, wherein the support surface is curved so that a central portion in the axial direction is farther from the backup roller than both end portions.   The fixing device according to claim 2, wherein the nip plate is curved by being deformed following the shape of the support surface.   The fixing device according to claim 2, wherein the stay is formed in a substantially U shape that is asymmetrical when viewed from the axial direction. The heater is a heating element that emits radiant heat,
Between the heater and the stay, a reflecting plate that reflects radiant heat from the heater toward the nip plate is provided,
The reflector has a supported portion that is sandwiched between the nip plate and the stay,
The supported portion is curved at least at the time of fixing so that a central portion in the axial direction is farther from the backup roller than both ends. The fixing device described.   The fixing device according to claim 1, wherein the cylindrical member is made of metal. The backup roller has a metal shaft and a rubber layer covering the outer periphery of the shaft,
The fixing device according to claim 1, wherein the shaft has a straight shape.

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